The invention relates to motorcycles, and more specifically, to motorcycles having exhaust systems.
Known motorcycles include four-stroke internal combustion engines that include pistons reciprocating within cylinders defining combustion chambers. The pistons each execute four strokes for each cycle of the engine. The strokes are compression, expansion, exhaust, and intake. The piston moves in a first direction during the compression and exhaust strokes, and in a second opposite direction during the expansion and intake strokes.
Exhaust systems are connected to the cylinders in order to direct the exhaust and reduce engine noise. Exhaust systems usually include a muffler and headers, or exhaust pipes, that are connected between the cylinders and the muffler. When an exhaust valve opens to begin the exhaust stroke of the piston, pressure pulses are created by the burst of high-pressure gas that suddenly escapes out of the combustion chamber and into the exhaust system. The pressure pulses, or sound waves, travel through the headers to the muffler where the amplitudes of the pressure pulses are reduced.
The present invention is directed to an exhaust system that improves engine power by receiving pressure pulses from an engine at uneven time intervals and delivering the pressure pulses to a common muffler at even time intervals. By delivering the pressure pulse to the muffler at even time intervals, the torque and power of the engine is increased for a range of engine speeds. In addition, a smaller capacity muffler may be used, because when the pulses reach the muffler at evenly-spaced time intervals, the pressure pulses evenly share the muffler.
One embodiment of the present invention is an exhaust system for a four-stroke engine. The engine includes first and second cylinders capable of producing pressure pulses. The engine includes a 360 degree cycle that begins with a first pressure pulse produced by the first cylinder, includes a second pressure pulse produced by the second cylinder, and ends with a next consecutive pressure pulse produced by the first cylinder. The phase difference between the production of the first pressure pulse and the production of the second pressure pulse is substantially less than 180 degrees. The exhaust system includes a muffler and first and second headers. The first header conducts the first pressure pulse from the first cylinder to the muffler, and the second header conducts the second pressure pulse from the second cylinder to the muffler. The first and second headers are configured such that, while the engine operates in a range of engine speeds, the first and second pressure pulses enter the muffler substantially 180 degrees out of phase with each other to improve the power of the engine within the range of normal engine operating speeds.
Another embodiment of the invention includes a method for designing an exhaust system for a motorcycle including an engine. The method includes determining a first phase difference between the production of a first pressure pulse and the production of a second pressure pulse, and configuring first and second headers to maximize a phase difference between the first and second pressure pulses at the muffler for a range of engine speeds such that, while the engine operates in the range of engine speeds, the first and second pressure pulses enter the muffler at substantially 180 degrees out of phase with each other to increase the power of the engine within the range of engine cycle speeds.
One exhaust system that embodies the invention is used with a four-stroke 45 degree V-twin engine having first and second cylinders that generate exhaust pulses at uneven time intervals with respect to each other. The exhaust system includes a muffler and first and second exhaust pipes that communicate between the mufflers and the first and second cylinders, respectively. The first and second pipes are sized and shaped to deliver the exhaust pulses to the muffler at even time intervals with respect to each other in a selected range of normal operating speeds.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.